Description

Since 17.0, when running tm expand on any task, the task fails (at least on gemini-2.5-pro) with:

Error expanding task 2: AI response contained potential subtasks, but none passed validation.

I have to manually add --prompt="details field must be string, not object"
 every time I expand or else it fails.

Steps to Reproduce

1. Run tm expand with model set to gemini-2.5-pro (submitter has not tested other models)

Expected Behavior

Subtasks are generated.

Actual Behavior

Subtask generation fails with [WARN] - Field 'details': Expected string, received object

Environment

• Task Master version: since 17.0
• Node.js version:
• Operating system:
• IDE (if applicable): Cursor

Additional Context

Model config was set to gemini-2.5-pro-05-06